Trace elements are widely used in industry and for medicinal purposes. Platinum, mercury, cadmium and lead are used in the plating industry, for example, to make electrodes for batteries and lamps. Compounds of these metals are used as catalysts for making varnish and paint compositions.
Waste waters from mining and public utilities also contain toxic heavy metals or their compounds. In addition, disposal of radionuclides from aqueous wastes of nuclear power plants is an important problem.
Disposal of wastes from these industries presents an ecological problem, particularly when the heavy metals are in the form of organic compounds or complexes, such as methylated mercury or lead. Organometallic compounds in waste waters are generally considered more objectionable than inorganic metal compounds or elemental metals because consumption of waters, containing organometallic compounds, by humans or domestic animals results in absorption and accumulation of relatively large amounts of heavy metal compounds in the organs of the animals, which consume the water. Organometallic compounds are absorbed from the intestinal tract much more readily than inorganic metal compounds or the free metals themselves. Moreover, organometallic compounds can cross the blood-brain barrier, accumulate in nervous tissue and cause disorders of the nervous system. Therefore, there is considerable interest in processes for removing toxic or objectionable heavy metal species from waste waters.
Summers et al., "Volatilization of Mercuric Chloride by Mercury-Resistant Plasmid-Bearing Strains of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa," J. Bacteriol., vol. 113 (1973), pages 1070-1072, have recited that strains PU21/FP, PU21/Stone and PU21/PS18 of Pseudomonas aeruginosa appear to convert mercuric chloride to elemental mercury, or another mercurial composition, which is volatile and soluble in organic solvents.
Chakrabarty et al. (U.S. Pat. No. 3,923,597) have proposed using genetically-engineered Pseudomonas bacteria to concentrate mercury or its compounds from liquid streams.
Walker et al., "Mercury-Resistant Bacteria and Petroleum Degradation," Appl. Microbiol., vol. 27 (1974), pages 285-287 and Kondo et al., "Mercury and Cadmium Resistances Mediated by the Penicillinase Plasmid in Staphylococcus aureus," J. Bacteriol., vol. 117 (1974), pages 1-7, recite characteristics of mercury-resistant organisms.
Bopp, in U.S. Pat. No. 4,468,461, has proposed using Pseudomonas fluorescens NRRL B-12596 to reduce chromate ions to chromic ions in aqueous solution. The chromic ions are precipitated at about neutral pH.
Kauffman et al. (U.S. Pat. No. 4,519,912) and Bakldwin et al. (U.S. Pat. No. 4,519,913) have proposed removing objectionable water-soluble species from aqueous solutions by treatment with various bacterial organisms. The proposed processes rely upon reduction of the ionic species to a corresponding elemental metal.
It is therefore apparent that removal of objectionable and toxic ionic or organometallic species of heavy metals from waste waters is of continuing importance in recycling of waste waters to provide water supplies, which are safe for drinking or industrial uses.
It is an object of this invention to provide processes by which toxic and objectionable heavy metal species can be removed from waste waters.